Abrasion resistant wire enamels



Patented Feb. 2, 1954 ABRASION RESISTANT ENAMELS Fred J. Emig and Michael J. Muth, Chicago,

assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Dela.-

ware

No Drawing. Application March 15, 1951, Serial No. 215,874

Claims.

This invention relates to wire enamels and more specifically to wire enamels which are highly resistant to abrasion and scraping.

In manufacturing armatures, stators, electroinagnets, coils and similar electrical equipment in which the wire is wound around a removable form or an iron core, the enameled wire repeatedly scrapes the metal parts of the winding mashine and the articleon which it is wound. If the insulating enamel coating is not highly resistant to scrape abrasion, it may be damaged and fail to perform its normal function satisfactorily.

Enameled wire is also subjected to vibration with resultant abrasion in many uses. It will be apparent that scrape abrasion resistance is highly desirable in all wires and conductors having a coating of enamel insulation.

An improvement in the abrasion resistance of polyvinyl formal wire enamels is disclosed in the copending patent application of E. Q. Bullock 0 vinyl acetal resin and a phenol-formaldehyde resin. The effect of abrasion resistance and other properties of a wire enamel by the addition of a polymer of ethylene is unpredictable, for example, if a dispersion of such a polymer is added to a nylon wire enamel, a heterogeneous 0 composition is produced, since the ingredients are incompatible. Nylon wire enamels have many valuable properties, and an improvement in their abrasion resistance is highly desirable. Such an improvement is also desirable in other wire enamels including oleoresinous enamels.

It is, therefore, the principal object of this invention to provide organic insulating enamels which, when applied by conventional means to a wire or similar conductor, are highly resistant to scrape abrasion. Another object is the provision of electrical conductors coated with such enamels. Other objects will appear as the description of the invention proceeds.

These objects are accomplished by dispersing a very small percentage of polytetrafluoroethyl ene, in the form of colloidal particles, in an organic insulating enamel which otherwise has a conventional composition comprising, as its resin, or an oleoresinous varnish, or va linear polyamide (nylon).

The linear polyamides shown in certain of the examples and referred to elsewhere herein are those described in U. S. Patents Nos. 2,071,250,-

p the most convenient form for use in this invention.

The invention is illustrated but not limited by the following examples in which the parts are by weight:

EXAMPLE I Nylon wire enamel High boiling petroleum hydrocarbon (B. P. 22 9294 C.). 206.00 Mixture of commercial phenols and cresols 518.00 Hexamethylene diammonium adipate polymer (nylon) 153.00

Polytetrafiuoroethylene dispersion in water Y 2.55

has. the following composition: Colloidal polytetrafluoroethylene 60.0.

The polytetrafiuoroethylene dispersion in water Wetting agent 0.6 Water 39.1

7 The wetting agent in this composition is the sodium salt of the sulfuric acid ester of a mix-: ture of long chain alcohols, predominately laurylalcohol. Other suitable wetting agents may .be 7 quantities sufiicient to stabilize the essential redient, p yvinyl formal type dispersion "j T substituted in The polytetrafiuoroethylene concentration is 1% based on the nylon polymer and 0.173% on the total composition.

The wire enamel of this example was made by dissolving the nylon polymer in a mixture of the hydrocarbon and cresylic acid, and thereafter mixing in the polytetrafluoroethylene dispersion with moderate agitation, followed by filtration to remove lumps and foreign matter.

Six coats of this wire enamel were applied to #18 gauge (American wire gauge) copper wire by conventional means which involve passing the wire through a bath of the wire enamel and then through an oven. Each coat was baked at 575- 585 F.

The test used for abrasion resistance is one adopted by the National Electrical Manufacturers Association and consistsess'entially of repeatedly scraping the surfaceof a coated wire with a rigid steel wire .016" in diameter, held at a right angle to the axis of the wire being tested and rubbed back and forth over th coated surface of the wire being tested under a weight to force the steel wire against the test section of the coated wire. The scrape abrasion resistance is rated by the number of cycles, i. e. one forward plus one backward scrape, required to wear through the enamel coating and cause a metal to metal contact as indicated by the completion of an electrical'circuit connected to the two wires.

Scrape abrasion tests as described above showed that test samples of the wire coated with this nylon wire enamel containing polytetrafluoroethylene withstood an average of 71 cycles under a 700 gram weight as compared to 20 cycles for the same product containing no polytetrafluoroethylene. Other properties were substantially equal.

Other suitable formulas for nylon wire enamels, to which'polytetrafluoroethylcne may be added as described above in the amount of 0.1% and 1% based on the film-forming solids, are disclosed in U. S. Patent No. 2,328,398.

EXAMPLEII' High boiling petroleum hydrocarbon (B. P. 229-294 C.)

7 206.00 Mixture of commercial phenols and cresols 518.00 Hexamethylene diammonium adipate polymer (nylon) 153.00

Polytetrafluoroethylene d is p e r s i o n in water 1.27

The above composition was prepared in the same manner as in Example I and contained the same aqueous dispersion of polytetrafluoroethylene, except that the polytetrafluoroethylene is present in the amount of 0.5% based on the no polytetrafluoroethylene. The other properties of the enamels were substantially equal.

4 EXAMPLE III oleoresinous wire enamel China-wood oil 233.73 Linseed oil 23.19 WG rosin 136.16 Metal resinate driers 10.20

High boiling high solvency petroleum hydrocarbons 404.01

The polytetrafluoroethylene dispersion has the same composition as that used in Example I. The polytetrafluoroethylene concentration is 1% based on the oleoresinous solids of the composition and 0.5% based on the total composition.

The wire enamel of this example was made by heating the oils and rosin to 560-585 F. with agitation, cooling to about 500 F., adding the metal resinates, and agitating to dissolve them. Then the hydrocarbons and phenolic inhibitor were added and mixed in uniformly; and the batch was cooled to room temperature. The polytetrafluoroethylene dispersion was added with moderate agitation and the batch was then illtered.

The resulting enamel was reduced with aboutv 1 volume of high solvency hydrocarbon solvent ior'each four volumes of wire enamel to obtain proper application viscosity.

Three coats of the thinned wire enamel were applied to #18 gauge (American wire gauge) copper wire, each coat being baked for 30-60 seconds in an oven at about 750 F. and further cured for about 4 hours at 265-275 F.

Scrape abrasion tests, as described in Example I, showed that test samples of wire coated with this oleoresinous wire enamel containing polytetrafluoroethylene withstood an average of 233 cycles under a 200 gram weight, as compared to 60 cycles for the same product containing no polytetrafluoroethylene. Other properties were substantially equal.

EXAMPLE IV Polyvinyl formal wire enamel High boiling petroleum hydrocarbon (B. P. 229-294? C.)

High solvency petroleum hydrocarbon (B. P. -184 C.) 125.50 Commercial cresylic acid 204.50 Polyvinyl formal resin 86.00 Phenol-formaldehyde resin 42.50

Polytetrafiuoroethylene d is p e r s i o n in water 2.13

The polytetrafluoroethylene concentration 1% based on the resin solids of the composition and 0.15% based on the total composition.

The wire enamel of this example was made by first dissolving the two resins in a mixture of the solvents, i. e. the two hydrocarbons and the cresylic acid. Then the polytetrafluoroethylene dispersion was added slowly, and moderate agitation was continued until the batch was homogeneous,

after which it was filtered.

The resulting wire enamel was applied by conventional means to #18 gauge (American wire gauge) copper wire and baked at 575-585 F. This coating process was repeated until six baked coats of enamel had been applied.

In scrape abrasion tests as described in Example I, samples of the wire coated with the polyvinyl formalphenol-formaldehyde wire enamel of this example containing polyterafiuoroethylene withstood an average of 145 cycles under a 700 gram weight as compared to an average of only '72 cycles for the same product containing no polytetrafluoroethylene. Other properties were substantially equal.

EXAMPLE V A wire enamel was made exactly as in Example IV except that 0.213 part of polytetrafluoroethylene dispersion was used in place of the 2.13 parts of Example IV. This lower concentration amounts to 0.1% polytetrafluoroethylene on the resin solids.

Samples of wire coated with the product of this example containing 0.1% polytetrafluoroethylene withstood an average of 92 scrape abrasion cycles under a 700 gram weight, as compared to an average of 72 cycles for the same product containing no polytetrafiuoroethylene. properties were substantially equal.

The 60% polytetrafluoroethylene dispersion shown in these examples is a convenient concentration, but the concentration of the added dispersion is not critical; and dispersions at other concentrations such as between 25% and 75% may be substituted on the basis of an equivalent polytetrafiuoroethylene content in the finished wire enamel. Also, dispersions of polytetrafluoroethylene in other materials such as volatile organic liquids (for instance, octane) may be used.

Polytetrafluoroethylene concentrations from .1% up to 1% based on the resin solids of wire enamel are shown in the examples. It is to be understood that this is the preferred range and that the resultant compositions represent a delicate balance among several important insulating enamel properties including compatibility, stability, applicability, electrical properties, abrasion resistance, adhesion to copper and other electrical conductors, etc. It will be obvious to those skilled in the art that higher percentages of polytetrafluoroethylene may be used where such high concentrations are compatible and are innocuous to the other essential properties of the resultant enamel.

The above examples illustrate the invention with respect to clear organic insulating enamels. It is to be understood, however, that pigments which do not impair the other essential properties of the enamels may be added, to prepare colored enamels or for other purposes. For example, in the preparation of a green enamel, phthalocyanine green pigment may be added to the extent of 1% of the entire composition. The pigment is usually dispersed or ground into Other a portionof the vehicle until a 'smooth dispersion is obtained and this dispersion is mixed uniformly in the main bulk of the enamel.

The nylon polymer used in Examples I and II maybe replaced by other similar polyamide polymers which are soluble in the type of solvents shown, such as the reaction product of hexamethylene diamine and sebacic acid.

A combination of drying oils (i. e. China-wood oil and linseed oil) is shown in Example III. Other drying oils may be used either individually or as mixtures of more than'one.

Natural or synthetic gums other than those specifically disclosed may be used, such as congo, amino-aldehyde, or alkyd resins.

In Examples IV and V polyvinyl formal resin is present in a weight proportion approximately twice that of the phenol-formaldehyde resin. The weight ratio of polyvinyl formal resin to phenol-formaldehyde resin may vary from about 1:1 to about 19:1. Any polyvinyl acetal or polyvinylal resin of the type described in U. S. Reissue No. 20,430 to Morrison et a1. or U. S. Patent No. 2,307,588 to Jackson and Hall may be substituted for the polyvinyl formal resin used in Examples IV and V.

In each of the examples, the solvent materials represent only one combination of organic liquids which is suitable for the purpose. It is not intended that the invention be limited to the par-' ticular combinations disclosed.

It will be obvious to those skilled in the art that infinite variation is possible within the spirit of this invention in the solvents and resins suitable for wire enamels which may be substituted for those disclosed in the examples. However, the combinations shown therein have been found to be particularly adaptable for organic insulating coatings (oleoresinous varnishes, linear polyamides and combinations of heat-hardenable phenol-formaldehyde resins with a polyvinyl formal resin) The wire enamels of this invention are useful wherever insulating type organic coating compositions are employed, but they ar particularly useful where high scrape abrasion resistance is required either in ultimate service or in the original fabrication of electrical apparatus from insulated components such as wire.

It is apparent that many widely different em- .bodiments of this invention may be made Without departing from the spirit and scope thereof, and therefore it is not intended to be limited except as indicated in the appended claims.

We claim:

1. An electrical insulating liquid organic coating composition consisting essentially of an organic film-forming material of the group which consists of (1) a combination of heat-hardenable phenol-formaldehyde resin and polyvinyl formal resin, (2)' a linear polyamide and (3) an oleoresinous varnish, and colloidal polytetrafluoroethylen dispersed uniformly throughout said coating composition, in a concentration between about 0.1% and about 1% by weight based on said film-forming material, to increase the scrape abrasion resistance.

2. The composition of claim 1 in which the organic film-forming material is a combination of heat-hardenable phenol-formaldehyde resin and polyvinyl formal resin. 7

3. The composition of claim 1 in which the organic film-forming material is a linear polyamide.

4. The composition of claim 1 in' which the organic film-forming material is oleoresinous.

. 5* An. electrical, conductor having a. dry admit.- ent coating. thereon or the composition or claim 1.

6. An electrical conductor having a dry caller.- ent coating thereon of the composition of claim 2.

7.. An. electrical conductor having. a. dry adherent coating thereon of the composition of claim 3. 8. An electrical conductor having a dry adhernt coating thereon of the composition of claim 4.

9. An abrasion resistant wire enamel havin the following, composition in Parts by weight:

water 2.55

10.. An electrical condocton having a. lo ked adherent coating or the compos tion or claim 9 omits surface.

FRED J. MICHAEL J'.

References Gitcd in the file or this patent UNITED STATES PA'IEN'IS Number Name Date 2,478,229 Berry Aug. 9, 1949 2,518,462 Gowing: et al'. Aug. 15, 1950 FQREIGN PATENTS Number Country Date 588,697 Great, Britain May 30, 194'? 

1. AN ELECTRICAL INSULTING LIQUID ORGANIC COATING COMPOSITION CONSISTING ESSENTIALLY OF AN ORGANIC FILM-FORMING MATERIAL OF THE GROUP WHICH CONSISTS OF (1) A COMBINATION OF HEAT-HARDENABLE PHENOL-DORMALDEHYDE RESIN AND POLYVINYL FORMAL RESIN, (2) A LINEAR POLYAMIDE AND (3) AN OLEORESINOUS VARNISH, AND COLLOIDAL POLYTETRAFLUOROETHYLENE DISPERSED UNIFORMLY THROUGHOUT SAID COATING COMPOSITON, IN A CONCENTRATION BETWEEN ABOUT 0.1% AND ABOUT 1% BY WEIGHT BASED ON SAID FILM-FORMING MATERIAL, TO INCREASE THE SCRAPE ABRASION RESISTANCE. 